The ambassador went on to say that the outcome would "profoundly shape the wider struggle and in turn the security of the world".

The US, he said, "should make adjustments in strategy" and redouble its efforts to succeed.

Mr Khalilzad outlined initiatives to try to stabilise Iraq, including a plan to reform Iraqi security ministries which he said should be ready by the end of the year.

He said the Iraqi government had agreed to develop a timeline for progress by the end of the year.

But the envoy made no mention of opening a dialogue with either Syria or Iran, which he accused of supporting armed groups in Iraq.

At the news conference Gen George Casey, the top US military commander in Iraq, said Iraqi security forces would be able to assume responsibility for the whole of Iraq within the next one-and-a-half years with minimal US help.

He said the process of building up Iraq's own security forces to a level appropriate for this was 75% complete.

Iraqi casualties

Gen Casey said that although the situation was "hard", Iraq was not "awash in sectarian violence".

He stated that 90% of sectarian attacks occurred in or near Baghdad, and 90% of all violence in five of the country's 18 provinces.

HAVE YOUR SAY

Having invaded the country I feel we are under some kind of obligation not just to abandon it